Field of the Invention
The present invention relates to a radiation detection apparatus for detecting radiation, and a radiation imaging system that uses the radiation detection apparatus to capture a radiographic image.
Description of the Related Art
In recent years, a flat panel type radiation detection apparatus that uses a sensor array in which conversion elements for converting radiation to an electrical signal are arranged in a two-dimensional array is spreading. Such a sensor array is commonly configured by making a two-dimensional arrangement of pixels (detecting units), which include a conversion element formed on a glass substrate and a switching element such as TFT for transferring an electrical signal converted by the conversion element to an external unit, into an array. Japanese Patent No. 4018725 (D1) recites a configuration that obtains an image by using such a sensor array. In the configuration recited in D1, a plurality of each of a gate driver for driving a switching element and a sense amplifier for detecting a charge are arranged on the substrate or outside of the glass substrate. The gate drivers drive the switching elements via driving signal lines, the sense amplifier reads electrical signals from the conversion elements via image signal lines, and an image is formed from the read electrical signals.
In an imaging room of a hospital or the like, an apparatus for emitting radiation, another examination apparatus, or the like are installed along with a radiation detection apparatus. There are cases where an apparatus that is used in accordance with a large amount of electric power is included in these apparatuses. In such an environment, electromagnetic energy from an apparatus that uses a large amount of electric power (hereinafter, a high-power apparatus) becomes magnetic field noise for other devices, and may cause a malfunction or a reduction of capabilities in these devices. When an alternating current magnetic field from outside is applied to a radiation detection apparatus for detecting a weak charge, horizontal stripe image noise referred to as line artifacts appear in a captured image. In particular, such noise is generated by a high-power apparatus described above, an inverter of an x-ray generator, or the like, and has a relatively low frequency band of approximately 1 kHz to 100 kHz. In addition, such an alternating current magnetic field may be from various directions due to usage conditions or installation conditions of the radiation detection apparatus and the high-power apparatus.
Japanese Patent Laid-Open No. 2012-119770 (D2) and Japanese Patent Laid-Open No. 2012-112726 (D3) propose configurations for reducing image noise due to an alternating current magnetic field as described above. D2 recites a configuration for adjusting, with respect to an alternating current magnetic field from outside at a specific frequency and a specific amplitude, a read time of a radiographic image and a dark image, and deleting an influence due to the alternating current magnetic field from a final image by subtraction processing. In addition, D3 recites a configuration for reducing an influence of electromagnetic noise by arranging a conductive member, a photoelectric conversion unit, and a scintillator in this order from a side where radiation of the radiation detection apparatus is irradiated.
However, in the technique of D2, if the frequency or the amplitude of the alternating current magnetic field differs between the time of obtaining the dark image and the time of obtaining the radiographic image, it is not possible to remove image noise due to the alternating current magnetic field in the subtraction processing. Furthermore, in D2, setting a time from the start of the obtainment of the dark image until the start of the obtainment of the radiographic image to be an integer multiple of the period of the external magnetic field is required. Therefore, there is the problem that it is necessary to delay the image obtainment interval to align with the period of the external magnetic field, and imaging speed decreases. In addition, there is the necessity to know the period of the external magnetic field in advance. In addition, in D3, while a reduction in relation to electromagnetic noise from a radiation incidence direction is possible, there is the problem that it is difficult to obtain an effect regarding an alternating current magnetic field from a direction horizontal to the radiation detection apparatus.